As disclosed in JP-A2009-103689, this sort of exhaust gas analyzing apparatus is used together with a constant volume sampling (CVS) mechanism that is configured to sample a total amount of exhaust gas emitted from an internal combustion engine, mix diluent gas such as air with the exhaust gas to produce mixed gas, and make a flow rate of the mixed gas constant.
Specifically, this exhaust gas analyzing apparatus is one that is provided with: a mixed gas containing bag that samples and contains the mixed gas; a diluent gas containing bag that samples and contains the diluent gas; and an analyzing mechanism that analyzes the gases contained in the respective containing bags to measure, for example, concentrations of measuring target components contained in the gases, and by subtracting the concentration of the measuring target component contained in the diluent gas from the concentration of the measuring target component contained in the mixed gas, makes a background correction to calculate concentration of the measuring target component contained in the exhaust gas.
According to the above-described exhaust gas analyzing apparatus, by diluting the exhaust gas emitted from the internal combustion engine, the concentration of moisture contained in the mixed gas can be reduced. This makes it less likely to cause condensation of the moisture, and therefore makes it possible to suppress a measurement error due to a gas concentration change caused by water condensation or a dissolution loss of a water-soluble component.
Meanwhile, to measure a fuel consumption ratio of a vehicle, it is necessary to measure the concentration of CO2, and to do so, for example, a non-dispersive infrared absorption (NDIR) method is used.
However, in future, it is expected that measurement accuracy required for the fuel consumption ratio measurement is increased, but the conventional measurement method cannot respond to the expectation. This is because moisture contained in exhaust gas, which has been considered to have no problem in conventionally required measurement accuracy, may cause an adverse influence in terms of a CO2 measurement level required in future.
Generally, in order to suppress the influence of moisture, a technique such as condensing the moisture to drain it is also possible; however, as described above, the CVS mechanism is based on the major premise that dilution prevents moisture from being condensed, and therefore it is also not possible to employ such a technique.